In recent years, as computers have developed and become popular, various kinds of information are put into digital data. As a device for storing such digital data, there is a storage device such as a magnetic tape and a magnetic disk. Because data to be stored has increased day by day and the amount thereof has become huge, a high-capacity storage system is required. Moreover, it is required to keep reliability while reducing the cost for storage devices. In addition, it is required that data can be retrieved later with ease. As a result, such a storage system is desired that is capable of automatically realizing increase of the storage capacity and performance thereof, that eliminates a duplicate of storage to reduce the cost for storage, and that has high redundancy.
Under such circumstances, in recent years, a content address storage system has been developed as shown in Patent Document 1. This content address storage system distributes and stores data into a plurality of storage devices, and specifies a storing position in which the data is stored based on a unique content address specified depending on the content of the data. To be specific, the content address storage system divides predetermined data into a plurality of fragments, adds a fragment that is redundant data thereto, and stores these fragments into a plurality of storage devices, respectively.
Later, by designating a content address, it is possible to retrieve data, that is, fragments stored in storing positions specified by the content address and restore the predetermined data before being divided from these fragments.
Further, the content address is generated so as to be unique depending on the content of data. Therefore, in the case of duplicated data, it is possible to acquire data having the same content with reference to data in the same storing position. Accordingly, it is not necessary to separately store duplicated data, and it is possible to eliminate duplicated recording and reduce the data capacity.
On the other hand, although having high redundancy as described above, the content address storage system also needs a replication of stored data. In this case, the content address storage system executes a process of retrieving a file system of a copy source and copying the file system to a file system that becomes a copy destination. Then, in the case of having executed the copying process once, the content address storage system compares the copy source file system with the copy destination file system and specifies an update file in the copy source file system, thereby being capable of reducing time required for the copying process.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. JP-A 2005-235171
However, in a case that a huge amount of files are stored in a file system to be copied, it takes much processing and time to execute a process of specifying an update file updated after the previous copying process. For example, in the case of specifying an update file by retrieving and comparing update time information of the respective files stored in the copy source file system and the copy destination file system, respectively, it is necessary to retrieve the update time information of all of the files. This causes a problem that time for the copying process and load of the system increase and the performance of the system decreases.